The bicycle frame of this invention is designed for heavy duty use and in particular is designed for use over rugged terrain where obstacles might otherwise contact and damage the sprocket on a conventionally constructed frame. The construction of the frame utilizes an interconnected single fore and double aft, loop assembly which provides a high degree of structural integrity. The high strength frame assembly is suitable for a high torque motor cycle, or other motor driven cycle.
Trail or enduro riding has become a popular sport for young cyclists. Specialty bicycles have been constructed to withstand the rigors of a competitive scrambler race over a dirt track with jumps and bumps in a close simulation of scrambler motorcycle racing. Cross country races, similar to motorcycle enduro races have also been devices for pedal bicycles. The bicycles for such competitive uses are conventional in configuration, but are substantially smaller than a standard 26 inch bicycle. Originally such bicycles were customized children's bicycles with small wheels and small frames which provided easy handling and high torque for quick accelerations and short hills. These features were incorporated into the specialty bicycles specifically designed for rugged use. The heavy duty frames, however, had essentially the same configuration as the conventional general use bicycles previously marketed. The frames included a head tube, pivotally supporting the front fork, a horizontal top tube, a nearly verticle seat tube, and a down tube forming a triangle structure with the top tube and seat tube. A pair of spaced seat stays and chain stays connected to the top and bottom of seat tube are joined at the axle of the rear wheel to provide triangular structures for support of the rear wheel. This conventional diamond pattern provides a light weight frame having a structural strength for most uses.
On such frames the sprocket journal is axially located at the interconnection juncture of the down tube, seat tube and chain stays. The sprocket and pedals are thereby exposed below the lowermost extension of the frame and are subject to contact with obstacles when used for trail or scrambler ridings.
The frame assembly of this invention is designed to utilize a looped tube concept for structural strength which is constructed to provide a sprocket location that is protected by the underside of the frame assembly. This configuration avoids a potentially dangerous contact of the sprocket with trail obstacles.
Variations in the particular configuration of the connected closed-loop frame components allow the sprocket to be positiond high in the frame for clearance of the sprocket and pedals above the lower most portion of the frame structure for exceptionally rugged trail use, or relatively low in the frame structure for clearance of the sprocket only, for more general trail use. In both variations, and in other contemplated embodiments between these extremes, the sprocket is protected from contact with trail obstacles.